The present invention relates to epoxy-functional silicones. More particularly, the present invention relates to epoxy-functional silicones which in combination with a sulfonium salt photoinitiator form one part UV-curable compositions.
Ultraviolet radiation curable compositions containing epoxy-functional silicones and 'onium salt photocatalysts are known in the art. Reference is made, for example, to U.S. Pat. No. 4,279,717 (Eckberg et al.); U.S. Pat. No. 4,576,999 (Eckberg); and U.S. Pat. No. 4,640,967 (Eckberg).
Current applications of iodonium salt catalyzed UV-cure epoxysilicones have been limited to two-part compositions because the iodonium salts designed for miscibility with epoxysilicone polymers do not possess sufficient thermal stability to permit packaging them with the reactive epoxysilicones. Even at low concentrations, the photocatalyst and various additive packages promote gelation of the catalyzed polymers in a few days to a few weeks depending on storage conditions. It is therefore necessary for the end user to add the iodonium photocatalyst to the epoxysilicone polymer immediately before use. While this has not been a problem for some coating applications, other UV cure coating applications such as conformal coatings, optical fiber coatings, and various high-viscosity silicone uses of this sort are best served with a one-component product. Such a product is easy to use, and, more importantly, avoids potential contamination from mixing equipment or the entrainment of persistent air bubbles in the coating bath.
Although the epoxy-functional silicones disclosed in the patents recited above form excellent UV-curable compositions, it is continually desirable to provide improved UV-curable epoxy-functional compositions. For example, it is particularly desirable to provide shelf stable one part UV curable epoxy-functional coating compositions.
In addition, it is desirable to provide epoxy-functional silicones which are more miscible with certain 'onium salt photoinitiators than currently used UV-curable epoxy-functional compositions.